linux-kernel - Re: [PATCH 3/3] Drivers: hv: vmbus: Make pannic reporting to be more useful

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Date:   Thu, 12 Oct 2017 15:39:37 +0200
From:   Vitaly Kuznetsov <vkuznets@...hat.com>
To:     kys@...hange.microsoft.com
Cc:     gregkh@...uxfoundation.org, linux-kernel@...r.kernel.org,
        devel@...uxdriverproject.org, olaf@...fle.de, apw@...onical.com,
        jasowang@...hat.com, leann.ogasawara@...onical.com,
        marcelo.cerri@...onical.com, sthemmin@...rosoft.com,
        kys@...rosoft.com
Subject: Re: [PATCH 3/3] Drivers: hv: vmbus: Make pannic reporting to be more useful

kys@...hange.microsoft.com writes:

> From: "K. Y. Srinivasan" <kys@...rosoft.com>
>
> Hyper-V allows the guest to report panic and the guest can pass additional
> information. All this is logged on the host. Currently Linux is passing back
> information that is not particularly useful. Make the following changes:
>
> 1. Windows uses crash MSR P0 to report bugcheck code. Follow the same
> convention for Linux as well.
> 2. It will be useful to know the gust ID of the Linux guest that has
> paniced. Pass back this information.
>
> These changes will help in better supporting Linux on Hyper-V
>
> Signed-off-by: K. Y. Srinivasan <kys@...rosoft.com>
> ---
>  arch/x86/hyperv/hv_init.c       | 11 +++++++----
>  arch/x86/include/asm/mshyperv.h |  2 +-
>  drivers/hv/vmbus_drv.c          |  4 ++--
>  3 files changed, 10 insertions(+), 7 deletions(-)
>
> diff --git a/arch/x86/hyperv/hv_init.c b/arch/x86/hyperv/hv_init.c
> index 1a8eb550c40f..cc30a094fb7c 100644
> --- a/arch/x86/hyperv/hv_init.c
> +++ b/arch/x86/hyperv/hv_init.c
> @@ -205,9 +205,10 @@ void hyperv_cleanup(void)
>  }
>  EXPORT_SYMBOL_GPL(hyperv_cleanup);
>
> -void hyperv_report_panic(struct pt_regs *regs)
> +void hyperv_report_panic(struct pt_regs *regs, long err)
>  {
>  	static bool panic_reported;
> +	u64 guest_id;
>
>  	/*
>  	 * We prefer to report panic on 'die' chain as we have proper
> @@ -218,9 +219,11 @@ void hyperv_report_panic(struct pt_regs *regs)
>  		return;
>  	panic_reported = true;
>
> -	wrmsrl(HV_X64_MSR_CRASH_P0, regs->ip);
> -	wrmsrl(HV_X64_MSR_CRASH_P1, regs->ax);
> -	wrmsrl(HV_X64_MSR_CRASH_P2, regs->bx);
> +	rdmsrl(HV_X64_MSR_GUEST_OS_ID, guest_id);
> +
> +	wrmsrl(HV_X64_MSR_CRASH_P0, err);
> +	wrmsrl(HV_X64_MSR_CRASH_P1, guest_id);

This is a constant we write in hyperv_init() (0x810000040e000000 for
Linux guests). Do I get it right that we need this to basically
distinguigh Windows guests crashes from Linux guest crashes in the log?

> +	wrmsrl(HV_X64_MSR_CRASH_P2, regs->ip);
>  	wrmsrl(HV_X64_MSR_CRASH_P3, regs->cx);
>  	wrmsrl(HV_X64_MSR_CRASH_P4, regs->dx);

We don't write ax and bx any more but write cx and dx. Not that I see
these regs really useful in the log but I'd change these to ax and bx
for consistency. Or mayme make it sp and ax?

>
> diff --git a/arch/x86/include/asm/mshyperv.h b/arch/x86/include/asm/mshyperv.h
> index 63cc96f064dc..dd2dc54ddf20 100644
> --- a/arch/x86/include/asm/mshyperv.h
> +++ b/arch/x86/include/asm/mshyperv.h
> @@ -311,7 +311,7 @@ static inline int hv_cpu_number_to_vp_number(int cpu_number)
>  void hyperv_init(void);
>  void hyperv_setup_mmu_ops(void);
>  void hyper_alloc_mmu(void);
> -void hyperv_report_panic(struct pt_regs *regs);
> +void hyperv_report_panic(struct pt_regs *regs, long err);
>  bool hv_is_hypercall_page_setup(void);
>  void hyperv_cleanup(void);
>  #else /* CONFIG_HYPERV */
> diff --git a/drivers/hv/vmbus_drv.c b/drivers/hv/vmbus_drv.c
> index e8cd19095212..852f6c628836 100644
> --- a/drivers/hv/vmbus_drv.c
> +++ b/drivers/hv/vmbus_drv.c
> @@ -65,7 +65,7 @@ static int hyperv_panic_event(struct notifier_block *nb, unsigned long val,
>
>  	regs = current_pt_regs();
>
> -	hyperv_report_panic(regs);
> +	hyperv_report_panic(regs, val);
>  	return NOTIFY_DONE;
>  }
>
> @@ -75,7 +75,7 @@ static int hyperv_die_event(struct notifier_block *nb, unsigned long val,
>  	struct die_args *die = (struct die_args *)args;
>  	struct pt_regs *regs = die->regs;
>
> -	hyperv_report_panic(regs);
> +	hyperv_report_panic(regs, val);
>  	return NOTIFY_DONE;
>  }

-- 
  Vitaly